System and method for carbon and syngas production

ABSTRACT

The present subject matter is directed to a system and method for producing carbon and syngas from carbon dioxide (CO2). The system includes a first reactor (7) for producing solid carbon (15) from a feed including CO2 and a volatile organic compound such as methane (1), and a second reactor (20) for producing syngas. Reactions in the first reactor (7) are conducted in a limited oxygen atmosphere. The second reactor (20) can use dry reforming, steam reforming, and/or partial oxidation reforming to produce the syngas (22).

TECHNICAL FIELD

The disclosure of the present patent application relates generally tohydrocarbon reforming. In particular, the disclosure relates to anapparatus and method for producing carbon and synthesis gas (syngas)from carbon dioxide (CO₂).

BACKGROUND ART

The reforming of methane is one of the most common industrial processesfor conversion of organic compounds (e.g., natural gas, which iscomposed primarily of methane) to synthesis gas (or “syngas”) using anoxidant. Syngas, which is primarily a mixture of hydrogen and carbonmonoxide, is an important feedstock for the production of a variety ofvalue-added chemicals, particularly hydrocarbon cuts, such as liquidtransportation fuels via Fischer-Tropsch synthesis, methanol anddimethyl ether, for example. The oxidant used for reforming of themethane determines its type. For example, in the case of steamreforming, steam is used as the oxidant. Steam reforming of methane usesthe following reaction, with ΔH₂₉₈=206 kJ/mol:CH₄+H₂O⇄CO+3H₂In partial oxidation, oxygen is used as an oxidant to produce syngas.Partial oxidation of methane is performed as follows, with ΔH₂₉₈=−36kJ/mol:CH₄+½O₂⇄CO+2H₂In dry reforming, carbon dioxide is utilized for oxidation purposes,with ΔH₂₉₈=247 kJ/mol:CH₄+CO₂⇄2CO+2H₂

Most research in methane reforming is directed towards improvement inthe reactant conversions, either through new catalyst materials or byoptimization of the operating conditions for a set objective. Recently,attention has been directed towards the “dry” reforming of methane dueto its ability to convert the two greenhouse gases (i.e., methane andcarbon dioxide) to syngas. However, the commercial applicability of dryreforming of methane has been very limited due to its inherent processlimitations, such as carbon deposition, high endothermicity of thereaction, and low values of synthesis gas yield ratios (H₂:CO ratio). Awell-accepted pathway for carbon formation, from methane, during the dryreforming reaction is given below:CH₄(s)→CH_(x)(s)+(4−x)H(s)  (1)CH_(x)(s)→C(s)+xH(s)  (2)H(s)+H(s)→H₂(g)  (3)A pathway for carbon formation, from carbon dioxide, during the dryreforming reaction is as follows:CO₂(g)↔CO(s)+O(s)  (4)CO(s)↔C(s)+O(s)  (5)O(s)+O(s)↔O₂(g)  (6)O(s)+H(s)+H(s)↔H₂O(g)  (7)

Thus far, the implementation of such dry reforming reactions hastypically suffered from carbon formation in the dry reforming reaction.The carbon formed on the surface of the catalyst deactivates thecatalyst due to formation of the carbonate phase, thus either requiringfrequent regeneration or, in certain cases, permanently destroying theactive site. It would be desirable to design a reactor for implementingthe dry reforming of methane with enhanced carbon dioxide fixation.Thus, a reactor system and process solving the aforementioned problemsis desired.

SUMMARY

The present subject matter is directed to a system and method forproducing carbon and syngas from carbon dioxide (CO₂). The systemincludes a first reactor for producing solid carbon from a feedincluding CO₂ and a volatile organic compound such as methane, andsecond reactor for producing syngas. Reactions in the first reactor areconducted in a limited oxygen atmosphere. The second reactor can use dryreforming, steam reforming, and/or partial oxidation reforming toproduce the syngas. This technique significantly increases CO₂ fixationby separating the production of solid carbon and syngas.

In an embodiment, the present subject matter is directed to a two-stagereactor system for capturing carbon and producing syngas, comprising:

a compression unit for compressing gas feed inputs;

a first reactor configured for receiving the compressed gas feed andproducing a solid carbon and unreacted gases;

an electrostatic precipitator configured for receiving the unreactedgases and separating a recovered solid carbon and a reactor feed gastherefrom;

a solid carbon and catalyst recovery unit configured for receiving thesolid carbon from the first reactor and the recovered solid carbon fromthe precipitator;

a heat exchanger configured for receiving the reactor feed gas from theprecipitator and providing high temperature reactor feed gases; and

a second reactor configured for receiving the high temperature reactorfeed gases from the heat exchanger and providing an output of hightemperature syngas back to the heat exchanger.

In an embodiment, the present subject matter is directed to a methodcomprising:

providing a compressed feed gas comprising carbon dioxide and at leastone volatile organic compound to a first reactor, the first reactorbeing a carbon generating reactor and comprising a first catalyst;

producing a gaseous product and a solid carbon in the first reactor, thegaseous product including at least one of flue gases, carbon dioxide,and unreacted methane;

removing the solid carbon from the first reactor;

feeding the gaseous product produced in the first reactor to a secondreactor to produce synthesis gas, the second reactor comprising a secondcatalyst, the second catalyst being different from the first catalyst.

These and other features of the present disclosure will become readilyapparent upon further review of the following specification anddrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a process flow diagram to depict operation of the carbongenerator (CARGEN) reactor, according to the present subject matter.

FIG. 2 shows a process flow diagram to depict operation of a two-reactorsetup for enhanced CO₂ fixation, according to the present subjectmatter.

FIG. 3 shows an embodiment according to Example 1 of the present subjectmatter.

FIG. 4 shows an embodiment according to Example 2 of the present subjectmatter.

FIG. 5 shows an embodiment according to Example 3 of the present subjectmatter.

FIG. 6 shows an embodiment according to Example 4 of the present subjectmatter.

FIG. 7 shows an embodiment according to Example 5 of the present subjectmatter.

FIG. 8 shows an embodiment according to Example 6 of the present subjectmatter.

FIG. 9 shows an embodiment according to Example 7 of the present subjectmatter.

FIG. 10 shows an embodiment according to Example 8 of the presentsubject matter.

Similar reference characters denote corresponding features consistentlythroughout the attached drawings.

DETAILED DESCRIPTION

According to an embodiment, the present subject matter relates to atwo-reactor system that provides enhanced carbon dioxide utilization forchemical and fuels processes, while ensuring fixation of CO₂ e.g.; theamount of CO₂ utilized is less than that generated during the process.The first reactor converts CH₄+CO₂ to solid carbon, while the secondreactor converts CH₄+CO₂ to syngas using a combined reforming reactionprocess. In view of the global concern of greenhouse gas emissions, thepresent system enhances overall CO₂ fixation, unlike conventional singlereactor reformer systems. From a CO₂ life cycle assessment (LCA) and aprocess integration point of view, the present subject matterfacilitates CO₂ utilization in methane reforming at fixation conditionswhile producing both solid carbon and syngas. The latter, syngas, is animportant feedstock for production of a variety of value-addedchemicals, as well as ultra-clean liquid fuels.

A combined reforming process in the present subject matter is aimed atreacting methane (or any other volatile organic compound) with CO₂, andoptionally other oxidants such as O₂, H₂O, or both to produce syngas. Asprovided herein, optimal operational conditions of temperature andpressure of the two reactors can be determined using a thermodynamicsequilibrium analysis. Any reaction feasible thermodynamically indicatesthat the reaction can be carried out, given that the hurdles associatedwith the process are tackled via the development of an efficientcatalyst and reactor orientation.

The present subject matter aims to maximize CO₂ fixation by optimizationof the operating conditions, which could maximize carbon formation inthe first reactor, i.e., the Carbon Generator Reactor (CARGEN), in thelimited presence of oxygen to drive the reaction auto-thermally. As thepartial combustion or partial oxidation reaction is an exothermicreaction, the CARGEN reactor hosts two main reactions concerning the CO₂fixation. The first reaction includes conversion of CO₂ to carbon. Thesecond reaction includes a partial oxidation reaction utilizing aportion of methane (or any other volatile organic compound) for partialcombustion to produce energy, among other products. The energy providedthrough partial oxidation reaction is more efficient compared to anyother form of heat transfer, as this energy is generated in-situ in theprocess itself.

According to an embodiment, the CARGEN reactor may be operated under lowtemperature and low/high pressure conditions, while the combinedreformer (second reactor) may be operated at high temperature andlow/high pressure conditions. By tapping the advantage of pressure andtemperature swings between the two reactor units, improvements occur inboth CO₂ fixation, as well as reduction in overall energy requirementsof the dual reactor setup. The present subject matter also utilizes workand energy extraction processes (like turbine, expanders etc.)associated with the change in pressure between the two reactors toovercome the pre-compression duty of the feed gas, at least partially.Thus, a unique synergism evident between the two reactors is beneficialfor saving carbon credits, as well as improving sustainability of theoverall process. In addition to the syngas generated from the secondreactor (reformer reactor), the present process also produces solidcarbon or carbonaceous material from the first reactor (CARGEN reactor).This carbonaceous product, which is produced as a part of the CO₂fixation process, is industrially valuable. In particular, thecarbonaceous product may serve as a starting material to produce manyvalue-added chemicals that can generate substantial revenue for theprocess plant. Non-limiting examples of the valuable chemicals includeactivated carbon, carbon black, carbon fiber, graphite of differentgrades, earthen materials, etc. This material can also be added tostructural materials like cement and concrete and in road tar or in waxpreparation as a part of the overall CO₂ capture process.

The present subject matter includes utilization of a dry reformingprocess for conversion of carbon dioxide to syngas and carbon. Thepresent subject matter enhances CO₂ fixation using a two-reactor setupor system. The reaction scheme is divided into two processes in separatereactors in series. The first reaction is targeted to capture CO₂ assolid carbon and the other to convert CO₂ to syngas. The present subjectmatter provides a systematic approach for CO₂ fixation.

The proposed scheme shows significant conversions of CO₂ to carbon atauto-thermal low temperature conditions (<773.15 K) in the first reactorof the two-reactor setup. The subsequent removal of solid carbon fromthe system (first reactor) enhances CO₂ conversions to syngas in thesecond reactor by thermodynamically pushing the reaction forward. Assuch, the carbon from the system is removed, which is incrediblybeneficial from the perspective of the CO₂ life cycle assessment (LCA).

There has been much research devoted to development of a novel class ofcatalyst targeted to resist the formation of carbon, and thus protect itfrom deactivation, on its surface to reduce downtime. However, suchcatalysts are very expensive and affect the overall economics of theprocess. The present subject matter is more economical because itinstead utilizes inexpensive catalysts in the first reactor. As anon-limiting example, the catalysts used may be the type of catalystsused in the reforming of biomass, such as calcite dolomite. Suchcatalysts are known to handle huge quantities of tar, a sticky materialcomprising solid carbon and other woody and inorganic materials.

After the reaction in the first reactor, the solid carbon is filtered.The remaining product gases are fed to a higher temperature secondreactor (a combined reformer) with the main focus of producing highquality syngas. Thermodynamic analysis of the results of operation ofthe second reactor shows that there is no carbon formation. This drivesthe reaction forward at much lesser energy requirements (approximately50 kJ less) and at relatively lower temperatures in comparison toconventional reformer setups. A substantial increase in the syngas yieldratio is also seen, which is not only beneficial for syngas productionfor Fischer Tropsch synthesis (requiring approximately a 2:1 H₂:COratio), but also for the hydrogen production (which requires high H₂:COratios).

In addition to the advantage of getting a higher H₂:CO ratio, asignificant increase in the methane and carbon dioxide conversion isalso seen at much lower operating temperatures. If a conventionalreforming setup was used, such effects would be obtained only at highertemperatures (almost 250° C.). The advantage of removing carbon in thefirst reformer helps to bring down the operating temperature in thesecond reactor significantly. As such, the present subject matter ismuch more energy efficient than the conventional single reactor setupoperated at higher temperatures to get similar levels of methane andcarbon dioxide conversions at zero carbon deposition.

FIG. 1 shows a conceptual process flow diagram to depict operation ofthe carbon generator (CARGEN) reactor or the first reactor in thetwo-reactor system of the present teachings. A compression unit 5receives inputs of methane 1, carbon dioxide 2, oxygen 3, and steam 4.The compression unit 5 provides an output 11 of compressed feed gas mixto the CARGEN reactor 6. The CARGEN reactor 6 provides an output of theunreacted gases 10, which goes to a cyclone or electrostaticprecipitator 12 which provides outputs of unreacted methane, carbondioxide, and steam 14 and recovered solid carbon 13. A solidcarbon/catalyst recovery unit 8 receives inputs of the spent catalystand solid carbon 7 from the CARGEN reactor 6 and the recovered solidcarbon 13 from the cyclone or electrostatic precipitator 12. Thecatalyst recovered is regenerated and fed back to the CARGEN reactor 6and the carbon is discarded to the discarded carbon and catalystcollector 9.

FIG. 2 is a non-limiting example of the two-reactor system according tothe present subject matter. FIG. 2 shows a compression unit 5 receivinginputs of methane 1, carbon dioxide 2, oxygen 3, and steam 4. Thecompression unit 5 provides an output 6 of compressed feed gas mix tothe CARGEN reactor 7. According to an embodiment, a work/energy recoveryunit 12 can be provided. The CARGEN reactor 7 can provide an output 10of unreacted gases from the CARGEN reactor at a high pressure to thework/energy recovery unit 12. The work/energy recovery unit 12 can thenoutput extracted work/energy 13 and provide feed to thecyclone/electrostatic precipitator 14. The cyclone/electrostaticprecipitator 14 provides outputs of recovered solid carbon 15 to thesolid carbon/catalyst recovery unit 8. The solid carbon/catalystrecovery unit 8 regenerates the catalyst (removes carbon from thecatalyst) and provides the catalyst back to the CARGEN reactor 7. Anycarbon and/or catalyst to be discarded is directed to the discardedcarbon/catalyst collector 9. The cyclone/electrostatic precipitator 14also outputs unreacted methane, carbon dioxide, and/or steam to a heatexchanger unit 16. From the heat exchanger unit 16, high temperature andlow pressure gases 17 are directed to the reformer reactor or secondreactor 20. An additional feed of methane, oxygen, and steam 18 combinewith the high temperature and low pressure gases from the heat exchangerunit 17 to serve as feed gases 19 to the reformer reactor 20. Thereformer reactor 20 then outputs high temperature syngas 21 to the heatexchanger unit 16. The heat exchanger unit outputs low temperaturesyngas 22.

In particular, the present subject matter is directed to a systematictwo-reactor setup to produce solid carbon and syngas separately in tworeactors. The operational conditions of each reactor are maintained atsuch conditions that could promote and target each of the products, andinhibit the other, separately. The present subject matter is alsodirected to a reactor for carbon dioxide and methane conversion to solidcarbon, referred to herein as Carbon Generator or “CARGEN”. The presentsubject matter is further directed to a systematic procedure to utilizeinexpensive catalyst in the CARGEN reactor for carbon deposition. Thepresent subject matter is also directed to a method for removal andregeneration of inexpensive catalyst from CARGEN reactor for acontinuous operation. The present subject matter is directed to areforming reactor that may operate on multiple feeds at differentoperational conditions. The present subject matter is further directedto a systematic method to protect an expensive reforming catalyst fromcarbon formation by alteration of feed composition which comes as aproduct from the CARGEN reactor. The present subject matter is alsodirected to a synergistic approach to integrate energy and extractuseful work from the streams exiting the CARGEN reactor.

It is noteworthy to understand the difference between the technology ofthe present subject matter and the conventional technology in terms ofthe perspective of the operation and targeted products. In the presentprocess, carbon dioxide is partially utilized in the first reactor byco-feeding methane and/or oxygen and/or steam together or separately tothe first reactor in order to produce solid carbon as product only. Theoperational conditions of the CARGEN reactor are chosen so that itpromotes solid carbon and does not promote syngas. Consequently, theobjective of the second reactor, a modified reforming reactor, is toproduce syngas from the raw gas (mainly unconverted methane, carbondioxide, steam, etc.) exiting the CARGEN reactor.

From the perspective of energy utilization and efficiency, the presentprocess produces an environment conducive to production of a singleproduct in two separate reactors. Additionally, the present approach mayutilize a relatively inexpensive catalyst (e.g., naturally occurringminerals such as calcite dolomite, coal, etc.) in the first reactor(CARGEN) to help in improving carbon formation. Essentially, the presentsubject matter targets only those catalysts which are known for theircoking tendency and as such, have been disregarded in the prior art foruse in the reforming process. On the other hand, due to significantreduction of carbon dioxide concentration from the first reactor, carbonformation tendency of the second reactor is almost eliminated.Therefore, an avenue is opened for the utilization of expensive, highstability, and high resistance catalyst for a longer operational time onstream.

Further, due to the unique method of segregation of operationalconditions in the two different reactors, the present system provides aunique opportunity for handling of the two products separately. Forinstance, the second reactor (which is mainly carbon formation free)does not need to undergo maintenance when the first reactor (CARGEN) isunder maintenance. During such a situation, more than one CARGEN reactorcould be added in parallel to ensure continuous operation.

Additionally, the catalyst removal process in the first reactor and thesecond reactor would be different, as the second reactor may utilize amore expensive catalyst and would not require many maintenance cycles,but could undergo regeneration more frequently. On the other hand, thefirst reactor may require many maintenance cycles and less frequentcatalyst regeneration. The difference in the method of handling ofcatalysts and operational conditions for production of the two productsseparately makes the present process unique when compared toconventional systems and methods.

In an embodiment, the remaining reactant gas mixture is used for thereforming reaction in the separate second reactor for carrying out thedry reforming reaction, while discarding the sacrificial surface(catalyst) in the CARGEN. In an embodiment, the remaining reactant gasmixture is used for the reforming reaction in the second reactor forcarrying out the combined dry reforming reaction and steam reformingreaction, while discarding the sacrificial surface (catalyst) in theCARGEN. In an embodiment, the remaining reactant gas mixture is used forthe reforming reaction in the second reactor for carrying out thecombined dry reforming, steam reforming, partial oxidation reforming, orany combination of the three, while discarding the sacrificial surface(catalyst) in the CARGEN.

In an embodiment, the inexpensive or sacrificial catalyst material isdiscarded in a batch-wise process while loading a new material. In anembodiment, the CARGEN is used for carbon capture while using theregenerated catalyst from a separate regenerator operated in parallelmode. In an embodiment, the sacrificial surface (catalyst) is treatedseparately to at least partially recover the catalyst while removingsolids (including carbon and sacrificed material).

The CARGEN may, optionally, be operated under no additional steam basis,as addition of steam increases both the energy demands and compromisesthe formation of coke. However, in an embodiment, steam may be added tothe second reformer (also called operated as combined Dry/Steamreforming) for increasing the conversion of the methane.

Addition of oxygen to both the CARGEN and/or to the combined reformerimproves carbon capture performance, as it increases carbon formation inthe CARGEN and also decreases the overall energy demands of the dualreactor setup.

Removal of the carbon (mechanically or with the spent catalyst) from theCARGEN pushes the reforming reaction forward in the second reactor(combined reformer) and thus subsequently increases the overall CO₂ andmethane conversions to syngas significantly.

In an embodiment, steam may be added to the second reactor to producehydrogen rich syngas for hydrogen production. Using steam in the secondreactor increases hydrogen in the system significantly.

As non-limiting examples, the product gas mixture from the secondreactor can at least be used as a feed stock for production of hydrogen,as a feed stock for Fischer Tropsch synthesis reaction, and as a feedstock for use as a source of energy in a hydrogen-based fuel cell. Asnon-limiting examples, the reactant gas may be an output product of afurnace in a process plant and may be a combination of the flue gasesand/or carbon dioxide and unreacted methane.

A carbon material produced at temperatures below 773 K and at anypressure (preferably close to 25 bar) may be separated and used for anyother process with or without the sacrificial material.

As non-limiting examples, the carbon material produced may be used inthe mortar/road tar production industry, used in the cement or concretemanufacturing industry, used as earthen material or as a potentialingredient of synthetic manure, used as a source of energy, and used asan energy carrier. In a non-limiting example, the carbon materialproduced may be used for industrial production of carbon black and/oractivated carbon, thus providing an alternative route to utilize carbondioxide for carbon black production. This consequently could serve astechnology for CO₂ capture by using a CARGEN reactor alone.

The overall process according to the present subject matter may be usedas a carbon capturing technology in a Gas to Liquid process, whichalready uses a conventional reformer setup, by addition of a new CARGENreactor upstream.

Synthesis gas produced from this process may be used for the productionof a variety of value-added chemicals. As non-limiting examples, thevalue-added chemicals may be alcohols, Di-methyl ether (DME),oxygenates, acids, etc.

The CARGEN reactor may be operated under auto-thermal conditions byusing oxygen as an additive for partial combustion (or oxidation) as theenergy source. Auto-thermal low temperature (below 773 K) is associatedwith zero carbon credits, and thus has more impact in fixation of CO₂from the life cycle of the process plant. The CARGEN reactor can beoperated under low temperature and low/high pressure conditions, whilethe second reactor can be operated at high temperature and low/highpressure conditions.

In an embodiment, the first reactor (the CARGEN reactor) comprises amechanical housing facility to receive methane, the carbon dioxide, andat least one more oxidant (oxygen etc). The first reactor may alsocomprise a housing/mechanism which actuates the removal and reloading(of a new batch or regenerated batch) of the sacrificial catalyticmaterial for carbon capture. The captured carbon on the sacrificialcatalyst material may be recovered partially or completely based on thecost benefit analysis.

A pretreatment process may be incorporated between the two reactors,which comprises of heating, cyclone separation, and mixing of anadditional oxidant (oxygen or steam or both with the gases leaving theCARGEN) for the second combined reformer. In such a process, thecatalyst chosen is compatible for combined reforming reaction in thesecond reactor.

In an embodiment, a pressure swing between the two reactors with a highpressure in first reactor and lower pressure in a second reactor cansignificantly affect carbon formation and energy requirements in theoverall system. In an embodiment, a pressure swing between the tworeactors with a lower pressure in first reactor and higher pressure in asecond reactor significantly reduces net energy demands, but decreasesoverall CO₂% conversion.

In an embodiment, the most optimum scheme as an outcome of the presentsubject matter is operation of the first reactor under auto-thermalconditions (by addition of pure oxygen along with CO₂ and methane) at apressure higher than the second reactor, with no addition of steam toboth the reactors. Steam may however be added only to increase hydrogencontent of product syngas if needed (for hydrogen production etc.).

In an embodiment, pressure swings between the reactors may be achievedby using an expander unit which decreases the pressure while derivinghigh quality shaft work, which may be used elsewhere in the plant. In anembodiment, pressure swings between the reactors may be achieved byusing a turbine generator unit which decreases the pressure whilederiving high quality shaft work, which could be used elsewhere in theplant.

The carbon dioxide capture process may be carried out in a continuousoperation by at least one additional train to switch back and forthduring cycles of maintenance and operations.

In an embodiment, the present process may be carried out by using anypotential volatile organic compound (e.g., ethanol, methanol, glyceroletc.) in place of methane or any such combinations.

In an embodiment, the present subject matter may be combined with anovel system for precipitating, aggregating, filtering, and interceptingcoke formation in order to efficiently utilize the sacrificial catalyticmaterial or to allow a better regeneration process.

In addition, the proposed configuration of the CARGEN reactor may beutilized for the production of a carbonaceous compound alone as carbondioxide fixation from the CARGEN process. In particular, this maypertain to industrial production of black ink for printers and pertainto industrial production of graphite of different grades, which may beused for manufacturing of cast iron/steel or batteries of differentgrades.

Furthermore, as shown in the specific case examples provided herein, theenergy utilization of the combined process is extremely low (almost 50%)compared to existing technologies. The present process also has thebenefit of high efficiency, as the present process has the capability toconvert more than 65% CO₂ per pass of reactor.

EXAMPLES Example 1

This embodiment is specific to the choice of feed to the reactors. FIG.3 shows a schematic of the two-reactor system. The first reactor(CARGEN) is dedicated to maximize the conversion of the carbon dioxideto solid carbon while maintaining operating conditions underauto-thermal conditions or mild exothermic conditions. The feed to thisreactor essentially includes methane, carbon dioxide, oxygen, and steamin a particular ratio. Steam can optionally be provided to the secondreactor. The second reactor (Syngas Reformer) is a reformer to producesyngas using a combined reforming reaction. The quality of producedsyngas can be appropriate for Fischer Tropsch synthesis or to producehydrogen.

This particular scenario is also a general case, which is valid forEXAMPLES 2-5. In this, the operating temperature of the first reactor(CARGEN unit) as shown in FIG. 3 , should be maintained below 773.15 Kfor enhanced conversion of the CO₂ in the feed gas mix (containing anycombination of feeds described in EXAMPLES 2-5) to carbon whileproducing negligible CO and H₂ generation to serve the purpose of theCARGEN unit (which is carbon generation). In this embodiment, however,the pressures of both the reactors should, be maintained constantwithout a pressure swing across the reactors. The temperature of thesecond reactor should be maintained above 973.15 K in order to maximizesyngas generation and get zero carbon formation.

The following case example relates to EXAMPLE 1 in which the feedcontains methane, carbon dioxide, steam, and oxygen in the compositionlisted in Table 1 below.

TABLE 1 Feed Composition and Operating Conditions of Reactors ComponentFed/ Operating Condition Value CH₄   1 mole H₂O  0.6 mole O₂  0.1 moleCO₂  0.6 mole T₁ (reactor 1) 693.15K P₁ (reactor 1) 25 bar T₂ (reactor2) 1093.15K  P₂ (reactor 2) 25 bar

TABLE 2 Product Composition of Reactors Product Reactor 1 CompositionReactor 2 Composition CH₄ 0.6516 0.2467 H₂O 1.2185 0.8695 O₂ 0 0 CO0.0025 0.4632 CO₂ 0.3895 0.3336 H₂ 0.0783 1.237 Carbon 0.5564 0 Energy(Kj) −1.074 176.04 CO₂% conversion 35 44.4

As can be seen in Table 2, the carbon formation in reactor 1 issignificantly high with CO₂% conversion of 35%, and the correspondingenergy requirement is −1.074 kJ. On the other hand, the carbon formationin reactor 2 is zero with an energy requirement of 176.04 kJ. Theoverall CO₂% conversion after reactor 2 is 44.4%.

Example 2

This embodiment is specific to the choice of feed to the reactors. FIG.4 shows a schematic of the two-reactor set up as described in EXAMPLE 1.The feed to this reactor essentially contains methane, carbon dioxide,and oxygen in different ratios. The gas mixture leaving the firstreactor (CARGEN unit) is sent to the second reactor, in which steam isalso added to increase the hydrogen content of the syngas produced fromthe reforming reaction (in reactor 2).

The following case example relates to EXAMPLE 2 in which the feed to thefirst reactor contains methane, carbon dioxide and oxygen, while steamis fed to the second reactor. The feed compositions are listed in Table3 below.

TABLE 3 Feed Composition and Operating Conditions of Reactors ComponentFed/ Operating Condition Value CH₄ (reactor 1)   1 mole O₂ (reactor 1) 0.1 mole CO₂ (reactor 1)  0.6 mole H₂O (reactor 2)  0.6 mole T₁(reactor 1) 693.15K P₁ (reactor 1) 25 bar T₂ (reactor 2) 1093.15K  P₂(reactor 2) 25 bar

TABLE 4 Product Composition of Reactors Product Reactor 1 CompositionReactor 2 Composition CH₄ 0.526209 0.146265 H₂O 0.887064 1.076974 O₂ 0 0CO 0.001769 0.330415 CO₂ 0.255583 0.296305 H₂ 0.06051 1.23049 Carbon0.8164 0 Energy (Kj) −11.9547 163.021 CO₂% conversion 57.4 50.6

As can be seen in Table 4, the carbon formation in reactor 1 is 0.8164moles with CO₂% conversion of 57.4%, and the corresponding energyrequirement is −11.9547 kJ. On the other hand, the carbon formation inreactor 2 is zero with an energy requirement of 163.021 kJ. The overallCO₂% conversion after reactor 2 is 50.6%. The drop-in CO₂% conversioncould be attributed to water gas shift reaction, which negativelyeffects the CO₂ conversion.

Example 3

This embodiment is specific to the choice of feed to the reactors. FIG.5 shows a schematic of the two-reactor set up as described in EXAMPLE 1.The feed to this reactor essentially contains methane, carbon dioxide,and oxygen in different ratios. The gas mixture leaving the firstreactor (CARGEN unit) is sent to the second reactor in which reformingreaction takes place at a different operating condition.

The following case example relates to EXAMPLE 3 in which the feed to thefirst reactor contains methane, carbon dioxide, and oxygen, while nooxidant is fed to the second reactor. The feed compositions are listedin Table 5 below.

TABLE 5 Feed Composition and Operating Conditions of Reactors ComponentFed/ Operating Condition Value CH₄ (reactor 1)   1 mole O₂ (reactor 1) 0.1 mole CO₂ (reactor 1)  0.6 mole T₁ (reactor 1) 693.15K P₁(reactor 1) 25 bar T₂ (reactor 2) 1093.15K  P₂ (reactor 2) 25 bar

TABLE 6 Product Composition of Reactors Product Reactor 1 CompositionReactor 2 Composition CH₄ 0.526209 0.2168 H₂O 0.887064 0.6095 O₂ 0 0 CO0.001769 0.343 CO₂ 0.255583 0.2238 H₂ 0.06051 0.9569 Carbon 0.8164 0Energy (Kj) −11.9547 132.53 CO₂% conversion 57.4 62.7

As can be seen in Table 6, the carbon formation in reactor 1 is 0.8164moles with CO₂% conversion of 57.4%, and the corresponding energyrequirement is −11.9547 kJ. On the other hand, the carbon formation inreactor 2 is zero with an energy requirement of 132.53 kJ. The overallCO₂% conversion after reactor 2 is at 62.7%. The increase in CO₂%conversion could be attributed to favorable forward dry reformingreaction and reverse water gas shift reaction due to removal of carbonformed in CARGEN reactor (reactor 1).

Example 4

This embodiment is specific to the choice of feed to the reactors. FIG.6 shows a schematic of the two-reactor set up as described in EXAMPLE 1.The feed to this reactor essentially contains methane, carbon dioxide,and oxygen in different ratios. The gas mixture leaving the firstreactor (CARGEN unit) is sent to the second reactor in which additionalmethane is added to increase carbon content of the syngas producedduring the combined reforming reaction.

The following case example relates to EXAMPLE 4 in which the feed to thefirst reactor contains methane, carbon dioxide, and oxygen, whileadditional methane is fed to the second reactor to increase carboncontent of the product syngas. The feed compositions are listed in Table7 below.

TABLE 7 Feed Composition and Operating Conditions of Reactors ComponentFed/ Operating Condition Value CH₄ (reactor 1)   1 mole O₂ (reactor 1) 0.1 mole CO₂ (reactor 1)  0.6 mole CH₄ (reactor 2)  0.3 mole T₁(reactor 1) 693.15K P₁ (reactor 1) 25 bar T₂ (reactor 2) 1093.15K  P₂(reactor 2) 25 bar

TABLE 8 Product Composition of Reactors Product Reactor 1 CompositionReactor 2 Composition CH₄ 0.526209 0.431079 H₂O 0.887064 0.540989 O₂ 0 0CO 0.001769 0.445953 CO₂ 0.255583 0.206529 H₂ 0.06051 1.19685 Carbon0.8164 0 Energy (Kj) −11.9547 166.0787 CO₂% conversion 57.4 65.6

As can be seen in Table 8, the carbon formation in reactor 1 is 0.8164moles with CO₂% conversion of 57.4%, and the corresponding energyrequirement is −11.9547 kJ. On the other hand, the carbon formation inthe reactor 2 is zero with an energy requirement of 166.0787 kJ. Theoverall CO₂% conversion after reactor 2 is at 65.6%. The increase inCO₂% conversion could be attributed to favorable forward dry reformingreaction and reverse water gas shift reaction due to removal of carbonformed in the CARGEN reactor (reactor 1) and addition of methane to thecombined reformer (second reactor).

Example 5

This embodiment is specific to the choice of feed to the reactors. FIG.7 shows a schematic of the two-reactor set up as described in EXAMPLE 1.The feed to this reactor essentially includes methane, carbon dioxide,steam, and oxygen in different ratios. The gas mixture leaving the firstreactor (CARGEN unit) is sent to the second reactor in which additionalmethane is added to increase carbon content of the syngas producedduring the combined reforming reaction.

The following case example relates to EXAMPLE 5, in which the feed tothe first reactor contains methane, carbon dioxide, steam, and oxygen,while additional methane is fed to the second reactor to increase carboncontent of the product syngas. The feed compositions are listed in Table9 below.

TABLE 9 Feed Composition and Operating Conditions of Reactors ComponentFed/ Operating Condition Value CH₄ (reactor 1)   1 mole O₂ (reactor 1) 0.1 mole CO₂ (reactor 1)  0.6 mole H₂O (reactor 1)  0.6 mole CH₄(reactor 2)  0.3 mole T₁ (reactor 1) 693.15K P₁ (reactor 1) 25 bar T₂(reactor 2) 1093.15K  P₂ (reactor 2) 25 bar

TABLE 10 Product Composition of Reactors Product Reactor 1 CompositionReactor 2 Composition CH₄ 0.651588 0.451764 H₂O 1.218518 0.794642 O₂ 0 0CO 0.00254 0.578313 CO₂ 0.389471 0.313522 H₂ 0.078305 1.50183 Carbon0.5564 0 Energy (Kj) −1.07446 211.7617 CO₂% conversion 35.1 47.74

As can be seen in Table 10, the carbon formation in reactor 1 is 0.5564moles with CO₂% conversion of 35.1%, and the corresponding energyrequirement is −1.07446 kJ. On the other hand, the carbon formation inreactor 2 is zero with an energy requirement of 211.7617 kJ. The overallCO₂% conversion after reactor 2 is at 47.74%. The CO₂% conversion isslightly increased due to the presence of a reasonable quantity of steamwhich produces CO₂ in addition to syngas upon reaction.

Example 6

This embodiment is specific to the operating conditions associated withthe operation of the dual reactor carbon fixation model described inEXAMPLES 1-5. As shown in FIG. 8 , the operating temperature of thefirst reactor (CARGEN unit) should be maintained below 773.15 K for atleast 40% conversion of CO₂ in the feed gas mix (containing anycombination of feeds described in EXAMPLES 1-5) to carbon, while havingnegligible (maximum one tenth of carbon generated) CO and H₂ generation.The temperature of the second reactor should be maintained above 973.15K for syngas generation and also to maintain zero carbon formation. Thepressures of both the reactors, however, are different with an effectivepressure swing between the two units. The pressure of the first reactor(CARGEN) should always be maintained above the pressure of the secondreactor (combined reformer).

The following case example relates to the EXAMPLE 6 in which thepressure in reactor 1 is maintained above the pressure in reactor 2 toemphasize the effect of a pressure swing on the CO₂% conversion from theoverall system. As a case example, this system comprises of a feed tothe first reactor containing methane, carbon dioxide, and oxygen, whileadditional steam is fed to the second reactor to increase the syngasyield ratio of the product syngas. The feed compositions are listed inTable 11 below.

TABLE 11 Feed Composition and Operating Conditions of the ReactorsComponent Fed/ Operating Condition Value CH₄ (reactor 1)   1 mole O₂(reactor 1)  0.1 mole CO₂ (reactor 1)  0.6 mole H₂O (reactor 2)  0.3moles T₁ (reactor 1) 693.15K P₁ (reactor 1) 25 bar T₂ (reactor 2)1093.15K  P₂ (reactor 2) 15 bar

TABLE 12 Product Composition of Reactors Product Reactor 1 CompositionReactor 2 Composition CH₄ 0.52621 0.11877 H₂O 0.88706 0.77963 O₂ 0 0 CO0.00177 0.40921 CO₂ 0.25558 0.25558 H₂ 0.25558 1.28282 Carbon 0.8164 0Energy (Kj) −11.9547 162.561 CO₂% conversion 57.4 57.4

As can be seen in Table 12, the carbon formation in reactor 1 is 0.8164moles with CO₂% conversion of 57.4%, and the corresponding energyrequirement is −11.9547 kJ. The carbon formation in reactor 2 is foundto be zero with an energy requirement of 162.561 kJ. The overall CO₂%conversion after reactor 2 is at 57.4%. In this scheme, no drop-in CO₂%conversion is seen between the two reactors, which can be attributed toa decrease in system pressure. Thus, a pressure swing between the tworeactors (with P₁>P₂) has a better effect on CO₂% conversion.

Example 7

This embodiment is specific to the operating conditions associated withthe operation of the dual reactor for carbon fixation model as describedin EXAMPLES 1-5. The operating temperature of the first reactor (CARGENunit) as shown in FIG. 9 should be maintained below 773.15 K foreffective conversion of CO₂ in the feed gas mix (containing anycombination of feeds described in EXAMPLES 1-5) to carbon, while havingnegligible CO and H₂ generation. The temperature of the second reactorshould be maintained above 973.15 K for syngas generation and zerocarbon formation. The maximum temperature of this reactor is recommendednot to exceed the conventional reformer setup (˜1173.15 K). This isbecause there is no additional benefit of going above these temperaturesin terms of energy requirements compared to conventional reformersetups.

The pressures of both the reactors, however, are different with aneffective pressure swing between the two units. The pressure of reactorone (CARGEN) should always be maintained below the pressure of thesecond reactor (combined reformer) with a pressure boost up between thetwo units. In order for sufficient work and energy extraction, asdescribed earlier, the pressure gradient is recommended to be about 10bar, which also improves the selective yields of carbon in the firstreactor and syngas in the second reactor.

The following case example relates to EXAMPLE 7 in which the pressure inthe first reactor (reactor 1) is maintained below the pressure in thesecond reactor (reactor 2) with a pressure boost up between the tworeactors to emphasize the effect of the pressure swing on the CO₂%conversion from the overall system. As a case example, this systemcomprises of a feed to the first reactor containing methane, carbondioxide, and oxygen, while additional steam is fed to the second reactorto increase the syngas yield ratio of the product syngas. The feedcompositions and operating conditions are listed in Table 13 below.

TABLE 13 Feed Composition and Operating Conditions of Reactors ComponentFed/ Operating Condition Value CH₄ (reactor 1)   1 mole O₂ (reactor 1) 0.1 mole CO₂ (reactor 1)  0.6 mole H₂O (reactor 2)  0.3 moles T₁(reactor 1) 693.15K P₁ (reactor 1) 15 bar T₂ (reactor 2) 1093.15K  P₂(reactor 2) 25 bar

TABLE 14 Product Composition of Reactors Product Reactor 1 CompositionReactor 2 Composition CH₄ 0.52196 0.18064 H₂O 0.87795 0.83345 O₂ 0 0 CO0.00232 0.34046 CO₂ 0.25987 0.26305 H₂ 0.07813 1.10527 Carbon 0.8159 0Energy (Kj) −11.1039 147.664 CO₂% conversion 56.6 56.1

As can be seen in Table 14, the carbon formation in reactor 1 is 0.8159moles with CO₂% conversion of 56.6%, and the corresponding energyrequirement is −11.1039 kJ. The carbon formation in reactor 2 is foundto be zero with an energy requirement of 147.664 kJ. The overall CO₂%conversion after reactor 2 is at 56.1%. This in comparison with theresults of case example of EXAMPLE 7 has seen a small drop-in CO₂%conversion. The drop-in CO₂% conversion in both the reactors show that arelatively lower pressure in reactor 1 compared to reactor 2 has nobenefit in terms of CO₂% conversion, however energy requirements havedropped significantly in reactor 2. It should also be noted that ahigher pressure in reactor 1 is favorable for better CO₂% conversion, aswe see a drop in about 1% in the CO₂% conversion between the twoschemes. The decrease in the energy requirements in the reactor 2 shouldhowever account for the carbon credits associated with the compressionduty in reactor 2 to make a fair comparison between the two schemes.

Example 8

This embodiment is specific to the operating conditions associated withthe operation of the dual reactor setup with addition of a work recoveryunit. The operating temperature of the first reactor (CARGEN unit) asshown in FIG. 10 should be maintained below 773.15 K (minimum 573.15 K)to get at least 40% CO₂ conversion in the feed gas mix (containing anycombination of feeds described in EXAMPLES 1-5) to carbon, while havingnegligible (maximum one tenth of the carbon produced) syngas generation.The temperature of the second reactor should be maintained above 973.15K for syngas generation and zero carbon formation. The pressures of bothreactors, however, are different with an effective pressure swingbetween the two units.

Due to the substantial pressure difference between the two units, anadditional expander or turbine unit could be added for generatingexternal work. The benefit of addition of the expander is not only toderive external work, but also to let down the pressure for the combinedreformer unit, as the performance of the combined reformer significantlyincreases with decrease in pressure. For this, the operating pressure ofthe first reactor (CARGEN) should always be maintained above thepressure of the second reactor (combined reformer).

It is to be understood that the two-stage methane reformer is notlimited to the specific embodiments described above, but encompasses anyand all embodiments within the scope of the generic language of thefollowing claims enabled by the embodiments described herein, orotherwise shown in the drawings or described above in terms sufficientto enable one of ordinary skill in the art to make and use the claimedsubject matter.

The invention claimed is:
 1. A two-stage reactor system comprising afirst reactor for a first stage and a second reactor for a second stage,for capturing carbon and producing syngas, comprising: a compressionunit for compressing gas feed inputs; the first reactor configured forreceiving the compressed gas feed and producing a solid carbon andunreacted gases; an electrostatic precipitator configured for receivingthe unreacted gases and separating a recovered solid carbon and areactor feed gas therefrom; a solid carbon and a catalyst recovery unitconfigured for receiving the solid carbon from the first reactor and therecovered solid carbon from the electrostatic precipitator; a heatexchanger configured for receiving the reactor feed gas from theprecipitator and providing high temperature reactor feed gases; and thesecond reactor configured for receiving the high temperature reactorfeed gases from the heat exchanger and providing an output of hightemperature syngas back to the heat exchanger, wherein the first reactorcomprises at least one first catalyst wherein the at least one firstcatalyst includes at least one of calcite, dolomite, and coal; whereinthe second reactor comprises at least one second catalyst, the at leastone second catalyst being different from the at least one first catalystand wherein the at least one second catalyst is a sacrificial surfacecatalyst that is removed without the use of additional steam.
 2. Thetwo-stage reactor system of claim 1, further comprising a work andenergy recovery unit configured for receiving unreacted gases from thefirst reactor, the work and energy recovery unit being selected from thegroup consisting of an expander and a turbine generator.
 3. Thetwo-stage reactor system of claim 1, further comprising a discardedcarbon and catalyst collector for collecting carbon and catalystdiscarded from the solid carbon and catalyst recovery unit.
 4. A methodcomprising providing a compressed feed gas comprising carbon dioxide andat least one volatile organic compound reactor to a first reactor, thefirst reactor being a carbon generating reactor and comprising a firstcatalyst; producing a gaseous product and a solid carbon in the firstreactor, the gaseous product including at least one of the flue gases,carbon dioxide, and an unreacted methane; removing the solid carbon fromthe first reactor; feeding the gaseous product produced in the firstreactor to a second reactor to produce synthesis gas, the second reactorcomprising a second catalyst, the second catalyst being different fromthe first catalyst, wherein the first reactor comprises at least onefirst catalyst wherein the at least one first catalyst includes at leastone of calcite, dolomite, and coal; wherein the second reactor comprisesat least one second catalyst, the at least one second catalyst beingdifferent from the at least one first catalyst and wherein the secondcatalyst is a sacrificial surface catalyst that is removed without theuse of additional steam.
 5. The method of claim 4, further comprisingpretreating the gaseous products produced in the first reactor prior tofeeding the gaseous products to the second reactor, the pretreatingcomprising subjecting the gaseous products to at least one of heatingand cyclone separation.
 6. The method of claim 4, further comprising:operating the first reactor at a first temperature; operating the secondreactor at a second temperature, the second temperature being higherthan the first temperature.
 7. The method of claim 6, wherein the firsttemperature is below about 773K.
 8. The method of claim 6, wherein thesecond temperature is above about 973K.
 9. The method of claim 4,further comprising: operating the first reactor at a first pressure;operating the second reactor at a second pressure, the first pressurebeing higher than the second pressure.
 10. The method of claim 4,further comprising: operating the first reactor at a first pressure;operating the second reactor at a second pressure, the first pressurebeing lower than the second pressure.
 11. The method of claim 4, whereinthe compressed feed gas further comprises at least one oxidant selectedfrom the group consisting of oxygen and steam.
 12. The method of claim4, wherein the volatile organic compound is selected from the groupconsisting of methane, ethanol, methanol, and glycerol.
 13. The methodof claim 4, further comprising adding at least one of an organicvolatile compound, oxygen, and steam to the second reactor.
 14. Themethod of claim 4, further comprising extracting work and energy from awork and energy recovery unit installed downstream of the first reactor,the work and energy recovery unit being selected from a group consistingof an expander and a turbine generator.